1. Field of the Invention
The present invention relates to structure of a magneto-resistive head using a magnetically stable spin bulb element used in a high-density hard disc and the like and to a production method thereof.
2. Description of the Related Art
With increase of the recording density of a magnetic disc apparatus, a spin bulb head in which a spin bulb film is used as a reading out element is now used in practice. The spin bulb film has a structure of two ferromagnetic films sandwiching non-magnetic Cu film. One of the ferromagnetic films called a fixed layer is in contact with an anti-ferromagnetic film and its magnetization direction is not changed by a signal magnetic field change from a magnetic recording medium because of the exchange coupling magnetic field with the anti-ferromagnetic film. The other ferromagnetic film called a free layer has a magnetization direction rotated by the signal magnetic field from the magnetic recording medium.
With change of the signal magnetic field from the magnetic recording medium, an angle defined by the fixed layer and the free layer is changed causing a resistance change due to the magneto-resistive effect. This resistance change is read out as a signal. It is known that linear feature of the signal is increased because magnetization of the free layer is directed vertical to the signal magnetic field direction in a bias state while magnetization of the fixed layer is directed in the signal magnetic field direction (or anti-parallel direction).
The fixed layer may be two ferromagnetic films anti-parallel to each other. In this case, Ru or the like is inserted between the two layers and the magnetization direction of the two-layered fixed layer is directed to anti-parallel by the anti-ferromagnetic coupling magnetic field generated via the Ru. This structure is called a layered ferri structure.
As the material of the free layer and the fixed layer, it is possible to use NiFe, Co, CoFe, and combination of these layered films. As the material of the anti-ferromagnetic film, it is possible to use MnPt, CrMnPt, NiMn, MnIr, NiO, and the like.
FIG. 4 shows, as an example, structure of a read-out element using the conventional spin bulb film. FIG. 4 shows the read-out element viewed from the magnetic recording medium. A spin bulb film MR is arranged between two magnetic shield films S1 and S2 via insulating films 11 and 12. At the both ends of the spin bulb film MR, a permanent magnet film D called a magnetic domain control film and an electrode film L for flowing signal detection current are arranged.
This structure is called “hard bias structure” and is disclosed in JP-A-3-125311. The free layer F has magnetization direction in X direction (track width direction) in a bias state while the fixed layer P has magnetization directed to the paper depth (MR height direction). A magnetic domain control film is provided to suppress Barkhausen noise caused by generation of a magnetic domain in the free layer F. The magnetic domain control film has a magnetization direction in X direction to assist the magnetization direction of the free layer F in a bias state.
As the material of the permanent magnet D, it is possible to use CoPt, CoCrPt, CoCrTa, and the like. It is known that these materials can exhibit a high coercive force when an undercoat film is provided and a two-layered structure of the permanent magnet film D and a Cr film as the undercoat film is used. JP-A-6-84145 discloses a structure in which the permanent magnet film D is replaced by a laminate film of a ferromagnetic film and an anti-ferromagnetic film. This ferromagnetic film in contact with the anti-ferromagnetic film and has a magnetization fixed in the track width direction by the exchange coupling magnetic field with the anti-ferromagnetic film, thereby exhibiting a function equivalent to the permanent magnet film. As the material of the anti-ferromagnetic film of the magnetic domain control film, it is possible to use a material identical to the anti-ferromagnetic film used for the spin bulb film MR.
To increase the recording density in the track width direction, it is necessary to reduce the space between the electrode films and reduce the magnetic reproduction width (track width). However, the hard bias structure causes a problem as follows. Firstly, FIG. 5 shows an X-direction component of a leak magnetic field from the magnetic domain control film D in respective track width direction positions of the free layer F. The leak magnetic field from the magnetic domain control film D is large at the element end in the proximity to the magnetic domain control film D and is reduced toward the element center portion.
FIG. 6 shows an output sensitivity of the element at respective track width direction positions. In the element end portion, the magnetic domain control magnetic field is large and the free layer magnetization is hardly rotated against the signal magnetic field from the medium. Thus, a low-sensitivity region exists. That is, an actual track width is increased with respect to the high-sensitivity region, which disturbs reduction of the track width.
Furthermore, as shown in FIG. 7, when the space between the electrode films L (space between magnetic domain control films) is reduced to a value identical to the low-sensitivity region width, the entire element becomes a low-sensitivity region, remarkably lowering the reproduction sensitivity. The low-sensitivity region width is almost identical distance between the end portion of the magnetic domain control film D and the magnetic shield film. This is because the leak magnetic field from the magnetic domain control film D can easily enters the magnetic shield film and the leak magnetic field from the magnetic control film D is reduced at a position where the distance from the magnetic domain control film D is greater than the distance from the end portion of the magnetic domain control film D to the magnetic shield film.
To solve this problem, JP-A-9-282618 discloses an electrode overlap structure. In the electrode overlap structure, the electrode films L are arranged so as to cover the spin bulb film MR and the distance between the electrode films L is smaller than the distance between the magnetic domain control films D. In this case, signal detection current flows to the electrode end portion having a smaller resistance than the element end portion having a low sensitivity. Accordingly, it is possible to reduce the reproduction output from the low-sensitivity region and to use only the high-sensitivity region. However, it is practically impossible to make zero the current flowing to the low-sensitivity region of the spin bulb film MR and the reproduction track width is increased than the distance between the electrodes.